Chem33-1, C-hour Problem Set 1

1. Which has the greater kinetic energy, an object with a mass of 2.0 kg and a velocity of 1.0 m/s, or an object with a mass of 1.0 kg and a velocity of 2.0 m/s? ANSWER: 1 2 1 ⎛ 1.0m ⎞ 2 1 2 1 ⎛ 2.0m ⎞2 KE = mv = x 2.0 kg x ⎜ ⎟ = 1.0 J; KE = mv = x 1.0 kg x ⎜ ⎟ = 2.0 J 2 2 ⎝ s ⎠ 2 2 ⎝ s ⎠ The 1.0 kg object with a velocity of 2.0 m/s has the greater kinetic energy. 2.Consider a mixture of air and gasoline vapor in a cylinder with a piston. The original volume is 40 cm3. If the combustion of this mixture releases 950 J of energy, to what volume will the gases expand against a constant pressure of 650 torr if all the energy of combustion is converted into work to push back the piston. ANSWER: In this problem q = w = -950 J 1 L atm − 950.J x = − 9.38 L atm of work done by the gases. 101.3 J - 650 w = − PΔV = - 9.38 L atm = atm x (V f - 0.040 L), V f - 0.040 = 11.0 L, Vf = 11.0 L 760 3.What is a state function? Enthalpy and internal energy are state functions as a direct consequence of the first law of thermodynamics. Why is this so? ANSWER: A state function is a function whose change depends only on the initial and final states and not on how one got from the initial to the final state. If H and E were not state functions, the law of conservation of energy (first law) would not be true.